The X-ray images make it obvious that animals live to eat. "We begin to see the body as an afterthought, following the mouth," ichthyologist Daniel Pauly writes in an essay in the book.

Determining how a creature ate, based on its teeth or jaw, is often speculative work. But sometimes an X-ray puts an animal's last meal right in front of your eyes--in the case of this hungry shark catfish, a few clams, which the catfish is adept at digesting.